A photonic integrated circuit (IC) utilizes optical communications to provide high speed data transfers (e.g., 112 Gbps using PAM4 signaling) between on-chip circuitry. To take advantage of the increased bandwidth afforded by an optical communication medium, the photonic IC may first need to convert binary input data from the electrical domain to the optical domain. More specifically, an electrical transmitter may generate an electrical signal based on the binary input data (e.g., using various signal modulation techniques) and an electro-optic modulator (EOM) may convert the electrical signal to a corresponding optical signal. The optical signal is then transmitted, over an optical communication medium (e.g., optical fiber), to an optical receiver which converts the optical signal back to an electrical signal to recover the binary input data.
The EOM produces the optical signal by encoding the input data onto an optical carrier (e.g., by modulating the amplitude or phase of light). Thus, the EOM may be a directly-modulated laser (DWL) or an external modulator coupled to a light source (e.g., continuous-wave laser or light-emitting diode). Examples of external modulators may include ring modulators (RMs) and electro-absorption modulators (EAMs). A modulator may include a waveguide to receive and modulate the optical carrier. For example, using the electro-optic effect, the modulator may modulate the amplitude (e.g., intensity) of the optical carrier by using an external electric field (e.g., corresponding to the electrical signal) to alter the refractive index of the waveguide. The change in refractive index is proportional to the electrical field.